Biomedical Signals

Prince E. Adjei

Kwame Nkrumah University of Science and Technology

Topic: Biomedical Signals Module 0: Introduction

Biosignal Processes And Analysis (BME 366)

Modules and Prerequisites

Modules:

0. Introduction

1. Signal Analysis: Time and Frequency Domain

2. Signal Processing: Filtering Methods

3. Biomedical Signal Processing: (ECG, EEG, EMG)

4. Advanced Topics: Wavelets, ML for Biosignals

Prerequisites:

•Fundamentals of Linear Algebra

•Fundamentals of Calculus

Biomedical Signal Processing

Analysis, interpretation, and manipulation of signals generated by

the body (biosignals) to extract meaningful information for

diagnostic, therapeutic, or research purposes.

Topics:

(1). Signals and Biosignals

(2). Signal taxonomy

(3). Data Acquisition Chain

(4). Sampling and Quantisation

(4). Oversampling

Learning Objectives

•Define what signals and biosignals are, with examples from ECG,

EEG, and EMG.

•Classify signals based on origin, dimensionality, and behavior

(deterministic vs stochastic).

•Understand the data-acquisition chain from biological event to

digital signal,

•Explain the principles of sampling and the Nyquist theorem, and

demonstrate the effects of aliasing.

•A signal is a function that conveys information about a physical

phenomenon, typically varying over time.

•Categories of Signals:

⚬Continuous-time vs Discrete-time signals

⚬Analog vs Digital signals

⚬Deterministic vs Random signals

⚬1-D vs multi-D signals

Fundamental Concepts of Signals

•A continuous-time signal is defined

for every instant in a continuous

domain, (e.g. x(t)), where time can

take any real value. Example ECG.

Continuous vs Discrete Time Signals

•A discrete-time signal is defined only at discrete time intervals (e.g.,

x[n]), where time is represented as a sequence of discrete values (e.g.,

integers). Example Digital Temperature.

[1]

1.Lin et. al (2023, November 29). Electrocardiogram Signal Denoising. Encyclopedia.

•Analog signals take on continuous

amplitude values.

•Digital signals take on discrete

amplitude values, typically in

binary form (0s and 1s).

Analog vs Digital Signals

•An ECG measured by electrodes is an analog signal, but when it

is stored on a computer, it is converted to a digital signal.

2. Unison Audio. (n.d.). Analog vs digital signals 101: Super important key factors

[2]

•Adeterministic signal is one whose behavior

is completely predictable (e.g., a sine wave).

•Arandom signal or stochastic signal has

some degree of randomness and uncertainty,

often described by probabilistic models.

Deterministic vs Random Time Signals

•ECG signals are more deterministic, while noise in an EEG can be

random.

[3]

3. Vasava A. (2020, October 6). What is a signal ?? Types of signals. Av Creations.

1D, 2D, Multi D

1D Signals (One-Dimensional)

•Vary along one independent variable, typically time.

•Represented as a single sequence of values or amplitude points.

2D Signals (Two-Dimensional)

•Vary along two independent variables, commonly time and space

or space in two directions (e.g., x and y).

•Represented as a matrix or grid.

Multi-Dimensional Signals

•Extend beyond two variables to include time, space, channel,

frequency, etc.

•Represented as multi-dimensional arrays or tensors.

•Amplitude: Height or value of the

signal at a given time

•Frequency: How often the signal

oscillates

•Phase: Relative position of the

waveform

•Duration: Period over which the

signal is defined

•Sampling rate: How frequently a

continuous signal is sampled to

convert to digital

Characteristics of Signals [4]

4. Mouser Electronics. (n.d.). Watch the feedback: An introduction to operational amplifiers.

What Is A Biosignal?

•Biosignals are signals that are generated by biological systems

such as living organisms.

•These signals could be electrical, chemical, or acoustic in origin.

•They are used in explaining and/or identifying pathological

conditions of the body.

Common examples of biosignals include:

•Electrocardiogram (ECG OR EKG)

•Electroencephalogram (EEG)

•Electromyogram (EMG) etc..

Other Biological Signals

•Electrooculogram (EOG) - electrical activity of the eye.

•Electrogastrogram (EGG) - electrical signal of the stomach

•Electroretinogram (ERG) - electrical signal of retina to light stimuli

•Phonocardiogram - vibration signal of the heart.

•Mechanomyogram (MMG) - mechanical vibrations of muscle

•Magnetoenephalogram (MEG) - magnetic field produced by brain

•Magnetocardiogram (MCG) - magnetic field produced by heart

Why We Process Biosignals

•Enhance Signal Quality: Remove noise, motion artifacts, and

baseline drift, improve clarity for better interpretation

•Extract Relevant Features

•Enable Diagnosis & Monitoring

•Prepare Data for Analysis & AI

•Reduce Data Complexity

Noise

•Noise in bio-signals refers to any unwanted interference or

disturbances that affect the quality of signals.

•Types of noise

⚬Random noise

⚬Physiological noise

⚬Structured noise

•Random noise refers to an interference

that arises from a random process Eg.

random noise, such as thermal noise in

electronic devices.

•A random signal is one that cannot be

determined from past values of the

signal.

Random Noise

[5]

5. Krishna, B A, Yadav G B P C S (2016). Random noise signal. In Performance comparison of different variable filters for noise cancellation

in real-time environment. ResearchGate.

Structured Noise

•Structured noise refers to unwanted signal components in a

system that have a specific, non-random pattern or structure, as

opposed to random noise (e.g., white noise), which lacks

predictability.

•Power-line interference at 50 Hz or 60 Hz is an example of

structured noise: The typical waveform of the interference is

known in advance.

Physioloigical Noise

•The appearance of signals from systems or processes other than

those of interest may be termed physiological interference; several

examples are listed below:

•EMG related to coughing, breathing, or squirming affecting the ECG.

•The maternal ECG getting added to the fetal ECG of interest.

•ECG interfering with the EEG.

•Breath, lung, or bowel sounds contaminating the heart sounds (PCG).

•Heart sounds getting mixed with breath or lung sounds.

Questions

1.Mention five (5) examples of signals

generated by biological systems.

2.How does processing biosignals help

in enabling diagnosis and monitoring?

3.What are the types of noise that affect

biosignals?

Signal Processing Pipeline

•The signal acquistion entails a four stage processing pipeline

Origin of Biosignals

•The action potential is the basic component of all bioelectrical

signals. It provides information on the nature of physiological activity

at the single-cell level.

•The action potential is the electrical signal that accompanies the

mechanical contraction of a single muscle cell when stimulated by an

electrical current (neural or external) (Originally reported in 1939)

Origin of Biosignals

•The action potential is caused by the flow of sodium (Na+),

potassium (K+), chloride (Cl-), and other ions across the cell

membrane.

•Action potentials are also associated with signals and messages

transmitted in the nervous system with no accompanying

contraction. Hodgkin and Huxley conducted pioneering work on

recording action potentials from a nerve fiber.

In their resting state, the membranes of

excitable cells readily permit the entry of K+ and

Cl-ions, but effectively block the entry of Na+

ions. The inability of Na+ to penetrate a cell

membrane results in the following:

•Na+ concentration inside the cell is far less

than that outside.

•The outside of the cell is more positive than

the inside of the cell

Origin of Biosignals

State: Polarised

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

[6]

Origin of Biosignals

•To balance the charge, additional K+ ions

enter the cell, causing a higher K+

concentration inside the cell than

outside.

•Charge balance cannot be reached due to

differences in membrane permeability for

the various ions.

•A state of equilibrium is established with a

potential difference, with the inside of the

cell being negative to the outside.

State: Polarised

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

[6]

Origin of Biosignals

•Stimulation causes the cell membrane to

allow Na

⁺

ions to rush in.

•This creates an ionic current, quickly

making the inside of the cell more positive.

•K

⁺

ions try to exit but can't keep up with

⁺

influx.

•The result is depolarization, where the

cell’s interior becomes positive.

•This marks the start of the action

potential, peaking at about +20 mV.

State: Depolarized

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

[6]

Origin of Biosignals

•After depolarization, the cell returns to its resting state via

repolarization.

•Repolarization primarily involves K

⁺

ions moving out of the cell

through voltage-dependent K

⁺

channels.

•Na

⁺

permeability decreases as the membrane potential peaks, while

⁺

permeability increases, driving the cell back to a negative internal

state.

•The Na⁺-K⁺pump restores ionic balance over a longer period but

plays a minor role in immediate repolarization.

State: Repolarized

Origin of Biosignals

•Nerve/muscle cells repolarize quickly (1–5 ms), while heart muscle

cells do so more slowly (150–300 ms).

•The action potential is all-or-none: it has a fixed shape and size once

triggered.

•After firing:

•The absolute refractory period (~1 ms) prevents any new action

potential.

•The relative refractory period (3–5 ms) allows a new action potential,

but only with a stronger stimulus.

State: Repolarized

Origin of Biosignals

7. Molecular Devices. (n.d.). What is an action potential?

[7]

•This image illustrates the phases of

an action potential, including

depolarization, repolarization, and

the return to resting membrane

potential.

•It highlights the rapid rise and fall

in membrane voltage as ions move

across the neuronal membrane,

enabling the transmission of

electrical signals.

Questions

1.Which ions are primarily involved in the

depolarization and repolarization

phases of an action potential?

2. In which state of the action potential

does the cell's interior become more

positive?

Origin of Biosignals

Cardiac: Signals related to the

electrical activity of the heart, such as

the electrocardiogram (ECG).

•The ECG reflects the electrical

activity of the heart.

•The pacemaker cells, known as the

sinoatrial (SA) node control the

heart rhythm.

•The PQRST represents one

complete ECG cycle.

•The ECG is the most commonly

known, recognized, and used

biomedical signal.

8. Lin H et. al, (2023, November 29). Electrocardiogram Signal Denoising. Encyclopedia

[8]

Electrocardiogram

•The rhythm of the heart in terms of beats

per minute (bpm) may be easily estimated

by counting the readily identifiable waves.

•More important is the fact that the ECG

waveshape is altered by cardiovascular

diseases and abnormalities such as

myocardial ischemia, infarction, and

ventricular hypertrophy.

8. Lin et. al, (2023, November 29). Electrocardiogram Signal Denoising. Encyclopedia

[8]

Overview of the Heart

•The heart is a four-chambered pump with two atria for

collection of blood and two ventricles for the pumping out of

blood.

•The resting or filling phase of a cardiac chamber is called

diastole; the contracting or pumping phase is called systole.

•The right atrium (or auricle) collects deoxygenated blood from

the superior and inferior vena cavae.

•During atrial contraction, blood is passed from the right atrium

to the right ventricle through the tricuspid valve.

Overview of the Heart

•During ventricular systole, the deoxygenated blood in the right

ventricle is pumped out through the pulmonary valve to the lungs for

oxygenation.

•The left atrium receives oxygenated blood from the lungs, which is

passed on during atrial contraction to the left ventricle, which is the

largest and most important cardiac chamber via the mitral (bicuspid)

valve.

•The left ventricle contracts the strongest among the cardiac

chambers, as it has to pump out the oxygenated blood through the

aortic valve and the aorta against the pressure of the rest of the

vascular system of the body.

Overview of the Heart

•The heart rate (HR) or cardiac rhythm is controlled by specialized

pacemaker cells that form the sinoatrial (SA) node located at the

junction of the superior vena cava and the right atrium.

•The firing rate of the SA node is controlled by the autonomic nervous

system (ANS), leading to the delivery of the neurotransmitters

acetylcholine or epinephrine.

•The normal (resting) heart rate is about 70 bpm. The heart rate is

lower during sleep, but abnormally low heart rates below 60 bpm

during activity could indicate a disorder called bradycardia.

•Coordinated electrical events and a specialized conduction system

intrinsic and unique to the heart play major roles in the rhythmic

contractile activity of the heart.

•The Sino-Atrial (SA) node is the basic, natural cardiac pacemaker

that triggers its train of action potentials.

The Electrical System of the Heart

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

[6]

The Electrical System of the Heart

•The action potential of the SA

node propagates through the rest

of the heart, causing a particular

pattern of excitation and

contraction.

•A schematic ECG signal is shown,

with labels showing the names

and durations of the various

component waves.

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

The Electrical System of the Heart

The sequence of events and waves in a cardiac

cycle is as follows:

1.The SA node fires.

2.Electrical activity is propagated through

the atrial musculature at comparatively low

rates, causing slow-moving depolarization

(contraction) of the atria. This results in the

P wave in the ECG. Due to the slow

contraction of the atria and their small size,

the P wave is a slow, low-amplitude wave,

with an amplitude of about 0.1 - 0.2 mV and

a duration of about 60 -80 ms.

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

[6]

The Electrical System of the Heart

3. The excitation wave faces a

propagation delay at the atrioventricular

(AV) node, which results in a normally

isoelectric segment of about 60 -80 ms

after the P wave in the ECG, known as the

PQ segment. The pause assists in the

completion of the transfer of blood from

the atria to the ventricles.

4. The AV node fires.

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

The Electrical System of the Heart

5. The His bundle, the bundle branches, and

the Purkinje system of specialized

conduction fibers propagate the stimulus

to the ventricles at a high rate.

6. The wave of stimulus spreads rapidly

from the apex of the heart upwards,

causing rapid depolarization

(contraction) of the ventricles. This results

in the QRS wave of the ECG —a sharp

biphasic or triphasic wave of about 1mV

amplitude and 80 ms duration.

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

The Electrical System of the Heart

7. The plateau portion of the action

potential causes a normally isoelectric

segment of about 100-120 ms after the

QRS, known as the ST segment; This is

because ventricular muscle cells possess

a relatively long action potential duration

of 300 - 350 ms.

8. Repolarization (relaxation) of the

ventricles causes the slow T wave,with an

amplitude of 0.1 - 0.3 mV and duration of

120 - 160 ms.

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

[6]

The Electrical System of the Heart

•Any disturbance in the regular rhythmic activity of the heart is called

arrhythmia.

•Cardiac arrhythmia may be caused by irregular firing patterns from the SA

node or by abnormal and additional pacing activity from other parts of the

heart.

•If the SA node is inactive or depressed, any one of the above tissues may take

over the role of the pacemaker or introduce ectopic beats. Different types of

abnormal rhythm (arrhythmia) result from variations in the site and frequency

of impulse formation.

The Electrical System of the Heart

•Premature ventricular contractions (PVCs) caused by ectopic foci on the

ventricles upset the regular rhythm and may lead to ventricular

dissociation and fibrillation —a state of disorganized contraction of the

ventricles independent of the atria —resulting in no effective pumping of

blood and possibly death.

•The waveshapes of PVCs are usually substantially different from those of

the normal beats of the same subject due to the different conduction

paths of the ectopic impulses and the associated abnormal contraction

events.

The Electrical System of the Heart [6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

The Electrical System of the Heart

•The ST segment, which is normally isoelectric (flat and in line with the

PQ segment) may be elevated or depressed due to myocardial

ischemia or due to myocardial infarction.

•Many other diseases cause specific changes in the ECG waveshape: the

ECG is an important signal that is useful in heart-rate (rhythm)

monitoring and the diagnosis of cardiovascular diseases.

•In clinical practice, the standard 12-lead ECG is obtained using four

limb leads and chest leads in six positions.

•The right legis used to place the reference (ground) electrode. The left

arm, right arm, and left leg are used to obtain leads I, II, and III.

The Electrical System of the Heart

•The illustration in the Figure shows the limb leads used to acquire the

commonly used lead II ECG. [6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

The Electrical System of the Heart

•The six chest leads (written as V1–

V6) are obtained from standardized

positions on the chest with Wilson’s

central terminal as the reference.

•The six chest leads permit viewing

the cardiac electrical vector from

different orientations in a cross-

sectional plane: V5 and V6 are most

sensitive to left ventricular activity;

V3 and V4 depict septal activity

best; V1 and V2 reflect well activity

in the right half of the heart.

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

Questions

1.What does the P wave in the ECG

represent?

2.What is the name of the isoelectric

segment after the QRS wave?

3.What is the purpose of the six chest

leads (V1–V6) in a standard 12-lead ECG?

Origin of Biosignals

Neural: Signals originating from the

brain or nervous system, such as the

electroencephalogram (EEG).

•The EEG reflects the electrical

activity of the brain.

•EEG primarily captures the summed

electrical activity of pyramidal

neurons in the cerebral cortex.

•These neurons are aligned in such a

way that their electrical fields add

up and become detectable through

the scalp.

[9]

9. Jin, C. (2014, September 3). Modeling the electroencephalogram (EEG) signals acquired during a seizure of a patient with epilepsy using

Fourier transformation. CJ Data Studio.

Electroencephalogram

•The EEG (popularly known as brain waves)

represents the electrical activity of the

brain. A few important aspects of the

organization of the brain are as follows.

•The main parts of the brain are the

cerebrum, the cerebellum, the brain stem

(including the midbrain, pons medulla,

and the reticular formation), and the

thalamus (between the midbrain and the

hemispheres)

•The cerebrum is divided into two

hemispheres, separated by a longitudinal

fissure across which there is a large

connective band of fibers known as the

corpus callosum.

[10

]

10. Michigan State University Libraries. (n.d.). Internal brain anatomy. In Foundations of neuroscience.

Electroencephalogram

•The outer surface of the cerebral hemispheres,

known as the cerebral cortex,is composed of

neurons(gray matter) in convoluted patterns

and separated into regions by fissures (sulci).

Beneath the cortex lie nerve fibers that lead to

other parts of the brain and the body (white

matter).

•Cortical potentials are generated due to

excitatory and inhibitory postsynaptic

potentials developed by the cell bodies and

dendrites of pyramidal neurons.

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

[6]

Electroencephalogram

•Physiological control processes, thought processes, and external stimuli

generate signals in the corresponding parts of the brain that may be recorded

at the scalp using surface electrodes.

•The scalp EEG is an average of the multifarious activities of many small zones

of the cortical surface beneath the electrode.

•In clinical practice, several channels of the EEG are recorded simultaneously

from various locations on the scalp for comparative analysis of activities in

different regions of the brain.

Electroencephalogram

•The International Federation of Societies for

Electroencephalography and Clinical

Neurophysiology recommended the 10-20

system of electrode placement for clinical

EEG recording, which is schematically

illustrated in Figure.

•The name 10-20 indicates the fact that the

electrodes along the midline are placed at

10%, 20%, 20%, 20%, 20%,and 10%of the

total nasion–inion distance; the other series

of electrodes are also placed at similar

fractional distances of the corresponding

reference distances.

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

Electroencephalogram

•The interelectrode distances are equal

along any anteroposterior or transverse

line, and electrode positioning is

symmetrical.

•EEG signals may be used to study the

nervous system,to monitor sleep stages,

for biofeedback and control,for brain–

computer interfacing, and for detection

or diagnosis of epilepsy(seizure).

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

•EEG signals exhibit several patterns of rhythmic

or periodic activity. (Note: The term rhythm

stands for different phenomena or events in the

ECG and the EEG.) The commonly used terms for

EEG frequency (f)bands are:

⚬Delta (δ): 0.5 ≤f < 4 ;

⚬Theta (θ): 4 ≤f < 7 Hz;

⚬Alpha (α): 7 ≤f≤12Hz; and

⚬Beta (β): f > 13 Hz.

⚬Gamma(γ) : f > 30 Hz.

Electrical Activity of the Brain [11]

11. iMotions. (n.d.). What is EEG (electroencephalography) and how does it work?

•The alpha rhythm is the principal resting rhythm

of the brain; it is common in wakeful, resting

adults, especiallyin the occipital area, with

bilateral synchrony.

•Auditory and mental arithmetic tasks with the

eyes closed lead to strong alpha waves, which

are suppressed when the eyes are opened (that

is, by visual stimulus).

Electrical Activity of the Brain

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE

Press.

[6]

•The alpha wave is replaced by

slower rhythms at various stages of

sleep.

•Theta waves appear at the beginning

stages of sleep.

•Delta waves appear at deep-sleep

stages.

•High-frequency beta waves appear

as background activity in tense and

anxious subjects.

Electrical Activity of the Brain

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE

Press.

Electrical Activity of the Brain

•In addition to the commonly studied rhythms mentioned above, the

gamma rhythm is defined as activity in the range 30 -80 Hz.

•The gamma rhythm is considered to be related to responses induced by

various types of sensory input or stimuli, active sensory processes

involving attention, and short-term memory processes

•The figure shows a 21-channel record of a patient with

a seizure starting at about the 50-s mark.

•The signal is characterized by a recruiting theta

rhythm at about 5 Hz in the channels labeled as T2, F8,

T4, and T6.

•Artifacts are evident in the signal due to muscle

activity (in T3, C3, and C4) and blinking of the eye (in

Fp1 and Fp2). Increased amounts of relatively high-

frequency activity are seen in several channels after

the 50-s mark related to the seizure.

Electroencephalogram

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE

Press.

[6]

Questions

1.What type of neurons primarily contribute

to the electrical activity captured by an

EEG?

2.What is the purpose of the 10-20 system for

electrode placement in clinical EEG

recording?

3.Which EEG rhythm is most common in

wakeful, resting adults and where is it

typically observed?

Muscular: Signals generated by muscle

activity, typically recorded using

electromyogram (EMG).

•The EMG reflects the electrical activity of

the muscle.

•The Central Nervous System (CNS),

comprising the brain, spinal cord, and

peripheral nerves, controls the action of

muscle fibres that typically results in

muscle movements.

Origin of Biosignals

•The EMG aids in the diagnosis of neuromuscular diseases.

EMG can be recorded by two methods: Surface and Intramuscular EMG

[12]

12. Shair, E. F., et. al (2016). Example of a raw EMG signal. In Auto-segmentation analysis of EMG signal for lifting muscle contraction activities.

Journal of Telecommunication, Electronic and Computer Engineering, 8(7), 17–20.

Electromyogram

•Skeletal muscles are made up of collections of motor units (MUs), each

of which consists of an anterior horn cell (or motoneuron or motor

neuron), its axon, and all muscle fibers innervated by that axon.

•Amotor unit is the smallest muscle unit that can be activated by

volitional effort. The constituent fibers of a motor unit are activated

synchronously.

•When stimulated by a neural signal, each motor unit contracts and

causes an electrical signal that is the summation of the action potentials

of all of its constituent cells.

Electromyogram

•This is known as the single-

motor-unit action potential

(SMUAP, or simply MUAP)

and may be recorded using

needle electrodes inserted

into the muscle region of

interest.

•Normal SMUAPs are usually biphasic or triphasic, 3 - 15 ms in duration, 100 -

300 µV in amplitude, and appear with frequency in the range of 6 - 30/s.

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

[6]

Electromyogram

•The figure illustrates simultaneous

recordings of the activities of a few motor

units from three channels of needle

electrodes: SMUAP trains recorded

simultaneously from three channels of

needle electrodes.

•Observe the different shapes of the same

•SMUAPs projected onto the axes of the

three channels. Three different motor units

are active over the duration of the signals

illustrated.

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

Electromyogram

(a) From the right deltoid of a normal subject,

male, 11 years; the SMUAPs are mostly biphasic,

with duration in the range 3 - 5 ms.

(b) From the deltoid of a six-month-old male

patient with brachial plexus injury (neuropathy);

the SMUAPs are polyphasic and large in

amplitude (800 µV ), and the same motor unit is

firing at a relatively high rate at low-to-medium

levels of effort.

patient with myopathy; the SMUAPs are

polyphasic and indicate early recruitment of

more motor units at a low level of effort. The

signals were recorded with gauge 20 needle

electrodes. The width of each grid box represents

aduration of 20 ms; its height represents an a

mplitude of 200 µV.

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE

Press.

Electromyogram

Muscular contraction levels are controlled in two ways:

•Spatial recruitment, by activating new motor units with increasing effort;

and

•Temporal recruitment, by increasing the frequency of discharge (firing

rate) of each motor unit with increasing effort.

Motor units are activated at different times and at different frequencies

causing asynchronous contraction. The twitches of individual motor units sum

and fuse to form tetanic contraction and increased force.

Weak volitional effort causes motor units to fire at about 5 - 15 pps (pulses per

second). As greater tension is developed, an interference pattern EMG is

obtained, with the constituent and active motor units firing in the range of 25 -

50 pps. Grouping of MUAPs has been observed as fatigue develops, leading to

decreased high-frequency content and increased amplitude in the EMG

Electromyogram

•Spatiotemporal summation of the

MUAPs of all of the active motor units give

rise to the EMG of the muscle.

•EMG signals recorded using surface

electrodes are complex signals

including interference patterns of

several MUAP trains are difficult

to analyze.

•An EMG signal indicates the level of

activity of a muscle, and may be used

to diagnose neuromuscular diseases

such as neuropathy and myopathy

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

Questions

1.What does the EMG measure in muscles?

2.What is a single-motor-unit action

potential (SMUAP)?

3.What is the difference between spatial

and temporal recruitment in muscle

contraction?

Dimension of Biosignals

Scalar signals

•These are single-valued signals that change over time, typically

recorded from one sensor and representing a specific physiological

measurement.

•A single measurement (e.g., temperature) is a scalar.

•In discrete-time form:

•→ x[nT] or x[n]

⚬n: sample number

⚬T: time interval between measurements

•In continuous-time (analog) form:

•→ x(t)

⚬Represents temperature as a continuous function of time

Dimension of Biosignals

Vector signals

•These are multi-component signals, often capturing directional or

multi-channel data.

•A blood pressure (BP) reading is a vector that includes two values:

⚬x1: systolic pressure, and x2: diastolic pressure

•Represented as a vector: x=[x1, x2]

BP data can be:

•A single vector (one-time measurement)

•An array of vectors (a series of readings)

•A plot over time, useful for observing trends in pressure

Dimension of Biosignals

Image signals

•Represent 2D spatial information for anatomical and functional

visualization.

•Characteristics: Static or dynamic 2D data, shows spatial

relationships across a plane.

•Examples: MRI: 2D slices of organs and tissues, and CT Scan: Cross-

sectional 2D images.

Volume signals

•Represent 3D spatial data, providing depth and detailed anatomy.

•Characteristics: Stacks of 2D images or full 3D datasets

•Examples: 3D Ultrasound, 3D fMRI

Data Acquisition Chain

[6]

6. Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study approach (2nd ed.). Wiley–IEEE Press.

IEEE & International Standards

Device Accuracy and Safety

•IEEE Std 1708-2014 (+1708a-2019) –Wearable, Cuffless BP

Devices

•⁠Defines test protocols, motion artifact tolerance, accuracy

limits, and calibration standards.

•Why it matters: Required for FDA submissions; ensures safe,

reliable blood pressure readings in wearable biosignal devices.

IEEE & International Standards

•Device Interoperability

ISO/IEEE 11073 Family –Health Device Communication Standards

•⁠Offers universal grammar for medical devices like ECGs, glucose

meters, and PPG sensors.

•Why it matters: Enables plug-and-play across platforms (e.g.,

Android, hospital systems), reducing manual data entry and

driver complexity.

IEEE & International Standards

•System-Level Data Exchange

HL7 FHIR (Fast Healthcare Interoperability Resources) –RESTful

Clinical APIs

•⁠Provides 150+ standard resource types (Patient, Observation,

Device, etc.) for healthcare data sharing.

•Why it matters: Powers real-time data integration into EHRs;

essential for scalable, regulatory-compliant systems.

Why These Standards Matter

1. Patient-safety baseline – IEEE 1708’s accuracy corridors and deformation-

testing catch dangerous drift in cuffless BP tech long before clinical trials

begin.

2.⁠ ⁠Plug-and-play ecosystems –IEEE 11073 removes the “driver soup”that

forces hospitals to hand-type vitals; devices advertise self-describing metrics

a manager already understands.

3.⁠ ⁠End-to-end traceability –FHIR’s resource IDs + provenance blocks let

auditors trace a heart-rate alert right back to the sensor and algorithm

version.

Why These Standards Matter

4.⁠ ⁠Reduced integration cost –Lack of standards is a well-documented

cause of manual data re-entry, care delays, and avoidable harm.

5.⁠ ⁠Regulatory momentum –FDA actively encourages standards-based

design to unlock interoperable device “ecosystems,”noting benefits

such as error reduction and innovation.

Other Fundamental Concepts

•Sampling:

The process of converting a continuous-time signal into a

discrete-time signal by measuring its value at regular intervals.

•Aliasing:

It occurs when a signal is undersampled Eg. If an ECG signal

containing high-frequency noise is undersampled, the noise may

appear as a lower frequency in the sampled signal, distorting the

signal’s representation.

Nyquist Theorem

•The Nyquist theorem states that to accurately sample and

reconstruct a continuous signal, the sampling frequency must be at

least twice the signal's highest frequency component.

•This is known as the minimum Nysuist rate. Mathematically:

fs ≥ 2fmax, to prevent loss of critical information (aliasing).

where: fs is the sampling frequency,

fmax is the highest frequency component of the

Quantization

•Quantization is the process of mapping a continuous range of

values (amplitudes of an analog signal) to a finite set of discrete

levels.

•The main purpose of quantization is to enable the representation

of analog signals in a form that can be easily processed, stored,

and transmitted in digital systems.

Quantization Noise

•Occurs during analog-to-digital conversion (ADC) of signals.

•Caused by rounding analog values to the nearest digital level.

•Appears as small, random errors (noise) in the digitized signal.

•More noticeable with low-resolution ADCs (fewer bits).

•Can distort low-amplitude signals like EEG or ECG.

•Not easily removed by filtering; reduces signal accuracy.

Oversampling

•Oversampling is sampling a signal at a frequency much higher

than the Nyquist rate (i.e., more than twice the maximum

frequency component of the signal).

•Oversampling Rate (OSR):

OSR=fsampling/2fmax

Signal-Noise Ratio(SNR).

•SNR is a measure of signal strength relative to background

noise.

•It tells us how clearly a signal can be detected or reconstructed.

•Mathematical defined us :

The 6 dB/bit Rule

•For an ideal ADC, each bit of resolution adds approximately 6 dB to

SNR.

Ghana Data Protection Act

Purpose & Scope

•Protects personal data of individuals in Ghana.

•Applies to all data controllers and processors—public and private.

•Regulated by the Data Protection Commission (DPC).

Duties of Data Controllers

•Register with the DPC before collecting personal data.

•Collect and process data lawfully, transparently, and fairly.

•Ensure data is accurate, relevant, and kept secure.

•Inform data subjects of purpose, rights, and intended uses.

•Limit retention to only as long as necessary.

Ghana Data Protection Act

Cross-Border Transfer of Data

Permitted only if:

•The data subject gives explicit consent, or

•The receiving country ensures adequate data protection.

•The Data Protection Commission may assess and approve transfers.

Penalties for Non-Compliance

•Administrative Sanctions by the Commission.

Fines:

•Up to 2,500 penalty units (~GHS 30,000+)

Imprisonment:

•Up to 5 years, or both fine and imprisonment.

Other consequences:

•Deregistration of the data controller,

•Civil liability for data subjects’ damages.

Ghana Data Protection Act

Ethical Responsibilities

•The privacy and dignity of individuals.

•Ensure transparency, accountability, and security in data handling.

•Support the rights of data subjects: access, correction, deletion, objection

Consent & Lawful Basis

•Must obtain informed, explicit consent from data subjects.

Consent is required before processing, except when:

•Required by law, in public interest, vital for health/life, or for legal obligations.

SUMMARY

•Biosignals are signals from the body (heart, brain, muscles, etc)

•Common types: ECG, EEG, EEG.

•Used to monitor health, detect diseases, support diagnosis and

treatment.

•Measured using sensors placed on or in the body.

•Why we process them: to remove noise, to extract useful patterns, to

prepare data for analysis

Recommended Text

•Rangayyan, R. M. (2015). Biomedical signal analysis: A case-study

approach (2nd ed.). IEEE Press Series in Biomedical Engineering.

Wiley–IEEE Press. ISBN: 978-0-470-01139-6.

•Palaniappan, R. (2011). Biological signal analysis. University of Essex

•Delgutte B (2007). Course materials for HST.582J / 6.555J / 16.456J,

Biomedical Signal and Image Processing, Spring 2007. MIT

OpenCourseWare, Massachusetts Institute of Technology.